Apparatus for dressing bonded grinding wheels



C. TlNDALL Jun 3, 1941.

APPARATUS FOR DRESSING BONDED GRINDTNG WHEELS Filed Sept. 28, 1957 2 Sheets-Sheet 1 INVENTOR.

CHHRLES TINDHLL, BY

fha/fnf 9 /m ATTORNEYS.

c. TINDALL 2,244,478

Filed Sept. 28, 1957 2 Sheets-Sheet 2 TTORNIS f5.

APPARATUS FOR DRESSING BONDED GRINDING WHEELSl June 3, 1941.

Patented June 3, 1941 APPARATUS FOR DRESSING BONDED GRINDING WIHEELS Charles Tindall, Natrona. Heights, Pa., assigner to Pittsburgh Plate Glass Company, Allegheny County, Pa., a corporation of Pennsylvania Application September .28, 1937, 'Serial No. 166,088

(Cl. til- 161) Claims.

The present invention relates to glass grinding apparatus and more particularly to an attachment for a glass grinding machine through the action of which the cutting surface ,of the grinding Wheel may be kept in condition for maximum grinding eiiiciency.

One object of the present invention is to provide an apparatus which will maintain the surface of bonded grinding wheels in operative condition and thereby prolong their effectiveness.

Another object of my invention is to provide an apparatus by means of which the necessary dressing of the grinding wheel may be performed while such wheel is in operative position on the grinding machine.

Other objects and advantages of my invention will become apparent from the following detailed description of a preferred embodiment thereof.

Brieiiy stated, my invention comprises a metal dressing tool mounted directly over the grinding wheel in such manner that it may be placed substantially in Contact with the upper surface thereof to remove progressively, successive layers of the composite grinding wheel when it is necessary so to do, in order to expose new particles of the abrasive material embedded therein. This dressing of the grinding surface is not accomplished by the tool alone, but a cutting compound is fed intermittently upon the grinding surface to fa.- cilitate the dressing action.

The loose abrasive type of grinding wheels, which are commonly used in the finishing of the edges of glass sheets, have always been objectionable to the industry. Not only is this method of grinding very costly, but it also requires continual attention to insure maximum cutting efiiciency. In addition, during the grinding operation, much of the loose abrasive collects on the polished surface of the glass and greatly increases the possibility of scratches or other damage thereto. Furthermore, after a period of time, the working surface of the cast iron Wheel becomes worn and the Wheel must be removed to be refaced, a costly operation requiring special equipment.

In order to eliminate these diiculties, bonded grinding wheels have been substituted for the loose abrasive method. A bonded grinding wheel,

, as contemplated by my invention, consists of abrasive particles embedded in and dispersed throughout a resinous composition, molded or otherwise formed into the desired size and shape. In certain types of bonded wheels the abrasive particles are merely cemented together by a resinous composition. It will be seen, therefore,

that the grinding surface of a bonded wheel presents a large number of abrasive particles partially surrounded by a molding composition, such as Bakelite or other synthetic resin.

A bonded grinding Wheel. provides for the edging of glass sheets in a much shorter period of time than is possible with the loose abrasive method, but the effective life of the grinding sui'- face of the bonded wheel is relatively short. This failure is explained by the fact that as the glass contacts the grinding surface, the abrasive particles gradually wear away or break loose from the bonding agent. At the same time the molding composition softens under frictional heat due to contact with the glass sheet and then glazes to produce a non-cutting surface. When the edges of laminated glass are being finished, the grinding wheel loses its efciency even more rapidly, for a portion of the plastic material uniting the glass plates together is retained by the grinding wheel to form a film which covers the abrasive particles. Manifestly a bonded Wheel in such condition is of no further use and it becomes necessary to dress the working surface in some way in order to restore it to its original condition.

My invention provides for an intermittent dressing of the grinding wheel While it is in operation and thus reduces, to aminimum, maintenance costs. At the same time, it is no longer necessary to remove the grinding` apparatus from the manufacturing line, with a subsequent loss of production.

A preferred embodiment of my invention is shown in the accompanying drawings, like numerals being employed to designate like parts and wherein: Fig. 1 is a side view partially in section and partially in elevation of a grinding apparatus embodying my invention; Fig. 2 is a plan view thereof; and Fig. 3 is a fragmentary detail view showing on an enlarged scale the dressing attachment in operating position.

In the drawings, the grinding apparatus includes a base I, composed of substantially vertical standards 2, braced and secured by horizontal members 3, and carries horizontal beams 4 secured in diverging relation thereupon, which in turn support a circular basin 5 provided with a drain 6. A support 'I is secured to one side of the base I by any suitable means and carries a motor 8, connected by means of a flexible coupling 9 to drive a horizontal shaft I0, projecting through a bearing I2. The shaft IIJ engages and drives a vertical shaft I3, mounted centrally of the base I, through suitable gears contained in and protected by a housing I4. The shaft I3 with a dressing attachment to be applied thereto whereby the grinding wheel I'I may be kept in operable condition. This attachment consists of a vertical member 25, adjustably secured between the beams 4 in a mounting 2'5 by means of a set screw 21. A tool holder 28 is positioned above the surface of the grinding wheel Il and provided with collars 29 through which it is supported on the vertical member 25. A locking screw 30 permits a vertical adjustment and insures secure positioning of the holder 28. The holder 28 includes side plates 32 which guide and support a dressing tool or bar 33. Screws 34 horizontally positioned in one of the side plates 32 serve to lock the dressing tool 33 in position in the holder 28. The dressing tool 33 may be adjusted vertically by the operation of screws 33 swivelly locked therein'and passing through the holder 28, the screws 3B having enlarged head portions 31 to facilitate their adjustment.

A reservoir 4D for a cutting compound 4I necessary to the dressing operation is also mounted upon the vertical member by means of bolts 43. The compound 4I flows through a chute 44 to the wheel Il and that now is controlled by a gate 45. Water, necessary for the dressing operation is supplied from a flexible conduit 46, which may be supported on the vertical member 25, and is delivered to the wheel I'I through a nozzle lll, a valve 48 enabling the flow of' water to be controlled.

In operation the grinding wheel Il does not have to'be removed from the apparatus until it is broken or becomes so thin that it must be replaced. When the grinding surface becomes glazed, the cutting compound 4l contained in the reservoir e9 is permitted to flow through the chute 411 by opening the gate i5 to the central portion of the grinding wheel and water is also supplied at this point. The dressing tool 33 is then lowered by means of the screws 3E until it engages approximately the wheel I'I and is locked in position by the screws 34. Rotation of the wheel Il causes the cutting compound and water to move against the dressing tool 33, while the centrifugal force of the wheel insures a uniform spread of the cutting compound lll over the grinding surface of the Wheel II. The coaction of the dressing tool 33 and the cutting compound 4I cuts away a portion of the bonding material surrounding the abrasive particles, thereby eliminating the glaze which has covered the grinding surface and also exposing new abrasive particles. The waste slurry of cutting compound is collected by the basin 5 and discharges through the drain 6. The dressing tool 33 is then raised from the grinding wheel and the flow of cutting compound and water halted to prevent too rapid deterioration of the Wheel.

It has been found that sand is a satisfactory cutting compound, although other materials. such as einery, could be used with equally good results. Under normal operating conditions, it is only necessary to apply the cutting compound and tool to the wheel twice an hour for a relatively short period of time. This dressing action maybe undertaken while the apparatus is still in use, and the edging of the glass need not be discontinued. It is, however, necessary to use sand or other cutting material, for the dressing tool when used alone, merely results in a heavier glaze being formed and no dressing action is effected.

It is to be understood that various changes in the shape, size and arrangement of parts may be resorted to without departing from the spirit of the invention or the scope of the following claims.

What I claim is:

l. In a glass grinding apparatus, a substantially horizontal driven grinding wheel composed of abrasive particles and relatively soft bonding material, a metallic bar having a lower edge portion disposed horizontally adjacent the upper horizontal surface of the grinding wheel and radially relative to the latter, means adjustably supporting the bar for setting the latter in or out of contact with the upper surface of the wheel whereby the bar scrapes the upper surface of the Wheel in response to rotation thereof, means for supplying upon the upper surface of the grinding wheel a quantity of loose sand to be agitated by the bar adjacent and under the latter and to be moved under the influence of centrifugal force of the wheel toward the periphery of the latter.

2. In a glass grinding apparatus, a rotatable grinding wheel composed of an organic binder having relatively hard abrasive particles bonded therein, a support for the wheel, means for abrading away the binder, together with foreign matter thereon, and exposing the abrasive particles in relief; said means including a feeder for supplying granular cutting material upon the surface of the wheel, a dressing member frictionally engageable with the surface of the wheel in response to rotation of the wheel, means for mounting the dressing member on the support and in frictional contact with the wheel whereby the granular material is frictionally agitated under the dressing member and upon the surface of the wheel.

CHARLES TINDALL. 

